The recently remarkable development in mechatronics technology extensively requires various sorts of linear motion guide units, especially, linear motion guide units of the type using rolling elements of cylindrical roller, which are also required to meet with the maintenance-free operation where there is no need of lubricant replenishment for considerably long service life even under severe operating conditions. Most conventional linear motion guide units are composed of an elongated guide rail and a slider that moves relatively to the guide way by virtue of more than one rolling element, which is allowed to roll through a recirculating circuit that is made up of a load-carrying race defined between the guide rail and the slider, and a non-loaded area including a return passage and turnaround passages made in the slider. With the prior linear motion guide units constructed as stated earlier, continuous application of lubricant on or between the load race and the rolling element is inevitable to continue maintaining an adequate lubricant film between the load race and the rolling element to keep them against metal-to-metal contact that might otherwise occur, thereby making sure of their high durability. To deal with the lubrication issue, most prior linear motion guide units have been ordinarily lubricated with periodic replenishment of lubricant so as to make certain of forming the lubricant film separating the rolling element from the circulating race. Recently advanced machines and instruments, nevertheless, are increasingly needed to make them virtually maintenance-free from many aspects of conserving energy as well as keeping running cost and maintenance cost of equipment reasonable. Correspondingly, the linear motion guide units built in the advanced machinery are also challenged to keep the consumption of lubricant to a minimum, along with keeping linear motion guide units virtually maintenance free.
In the commonly assigned Japanese Patent Laid-Open No. 2001-082469, there is disclosed a linear motion guide unit in which a return passage in a carriage of the slider is made of sintered resinous member of cellular or porous structure that is impregnated with lubricant to be applied on the rolling elements. The prior linear motion guide unit is comprised of an elongated guide rail, a slider movable lengthwise relative to the guide rail, and more than one rolling element allowed rolling into the load race defined between the guide rail and the slider from the non-loaded return passage cut in the slider, and vice versa in a recirculating manner. The return passage is constituted with a sleeve of sintered resinous member having cellular structure, which fits into a fore-and-aft hole made in the carriage of the slider. Oily lubricant or grease once soaked in the sintered resinous member preparatory to fit into the carriage is reserved or held in the cells or pores in the cellular structure. Oily ingredient of the lubricant is constantly applied on the rolling elements while rolling through inside the sleeve, and oil films around any rolling elements get lubricating smoothly the load-carrying surfaces or raceway grooves as the rolling elements run through load race, with accompanying reduced maintenance.
Another commonly assigned Japanese Patent Laid-Open No. H09-072335 discloses a linear motion guide unit in which a sleeve for a return passage fits into a fore-and-aft hole made in a carriage of the slider to provide the return passage. The sleeve is made easier to experience elastic deformation to absorb the frictional resistance occurring on the rolling elements, thereby ensuring smooth running of the rolling elements. With the linear motion guide unit constructed as recited just earlier, the rolling elements are made in the form of cylindrical roller while the return passage is defined by the sleeve that fits closely into the return hole cut in the carriage. The sleeve is made it possible to get elastic deformation, ensuring smooth traveling of the slider. Especially, as seen in FIGS. 11 to 13 in the cited disclosure, an ample clearance is left between the wall surface inside the return passage and the outside surface around the middle area of the sleeve to allow the sleeve to get elastically deformed therein and also reserve lubricant therein.
Another sort of linear motion guide means is disclosed in Japanese Patent Laid-Open No. H10-078032, in which there is used lubricant-containing polymer to lubricate the rolling element of ball. With the linear motion guide means recited now, a sleeve allowing the rolling elements running through is made of tubular composition of lubricant-containing polymer, which is composed of cylindrical skeleton cage of polyethylene high in stiffness or mechanical strength, the skeleton cage being made therein with lengthwise windows opened from the outside to the inside thereof and spaced away from one another at regular intervals around the circular surface of the skeleton cage, and lubricant-containing polymer segments that fit closely into the windows, one to each window. For production of the tubular composition of lubricant-containing polymer, the polyethylene skeleton cage prepared in advance by injection molding is positioned within a preselected mold held in any injection molding machine, and then molten lubricant-containing polymer is poured into the mold cavity, where it solidifies as it cooled, coming into joining integrally with the skeleton cage.
Another Japanese Patent Laid-Open No. 2001-248637 discloses a linear motion guide unit making it easier to ensure lubrication of circulating balls with lubricant that may be simply replenished from the outside of the guide unit, making certain of serving steadier functions in the long run even with no troublesome maintenance work. With the linear motion guide unit stated just earlier, the slider is composed of a carriage having return passages therein and end caps attached on forward and aft ends of the carriage. The return passages are each provided with a return sleeve that is lengthwise slit and lined with a lubricant applicator over the inside circular surface thereof. The fore-and-aft slit made in the return sleeve constitutes a groove that helps the lubricant spreads easier lengthwise from the lubricant applicator covering the fore-and-aft slit.
With the linear motion guide unit in which rollers are selected as the rolling elements, nevertheless, alignment problems to guide rollers in good rolling order without leaning in rolling posture are more encountered, compared with the construction using balls. Besides, the rollers have to be guided not only on their circular surfaces, but also on their axially opposite end surfaces. Conventionally, there is no linear motion guide unit constructed to meet with an aspect of allowing the rollers to roll through the recirculating circuit over a long-lasting service life with adequate application of lubricant, making certain of steady reliability of the maintenance-free on lubricant application.
With the prior linear motion guide units recited earlier, moreover, the return passage made in the carriage of the slider is defined by just sintered resinous member of cellular geometry, which is lack of mechanical stiffness enough to guide steadily the cylindrical rollers. The rollers, as opposed to the balls, need functioning on line-rolling contact around their circular surfaces without getting tilted in rolling posture. In other words, the rollers have to be not only born against their circular surfaces, but also guided in sliding manner on their axially opposite ends to get the slider moved steadily with smoothness, ensuring the long-lasting service life with stability. Thus, the prior linear motion guide units of the sort in which the return passage is made of only sintered resinous member of cellular geometry, because there is a scarcity of mechanical stiffness in the sintered resinous member, have been unsuited for making certain of smooth recirculation of the rollers. There, advanced technology has come to hope any linear motion guide unit in which the sleeve to define the return passage in the carriage of the slider is much raised in mechanical stiffness, even with simple in construction and easier to fit it into the slider as well as making sure of positive lubricant application to the rolling elements to render the maintenance-free operation steadier.
With the prior linear motion guide means recited earlier in which there is used lubricant-containing polymer sleeve to lubricate the rolling element of ball, it is needed to uniformly mix polymer with oily lubricant to prepare the lubricant-containing polymer and, moreover, the lubricant-containing polymer sleeve have to be molded integrally with the skeleton cage of a preselected material high in stiffness. Production of the lubricant-containing sleeve has thus required special equipment and complicated process.